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In other words, the P. oleracea extracts could improve daily gain of broilers. It was seen that the addition of different proportions of P. oleracea extracts had differenteffects on the BWG and FCR. Table 2 showed that 0.2% of P. oleracea extracts supplement could promote the growth performance of broilers on d 28 and 42, but the supplementation had no significant effects on broilers on d 14. In our later research, we will focus on the effect of P. oleracea extracts administered at different phases, to decide reasonable application of this herbadditive. Bai et al. (2003) stated that one of the shortcomings of herbal medicine as feed additive was excessive dosage. The general additive dosage was up to 1 to 2%. This dosage not only increases production cost, but also affects the nutrition ratio of feed. So it is suggestedthat a dosage lower than 0.5% would be appropriate. The current study showed that from d 14 to 28, the BWG of the group fed with 0.2% P. oleracea extract additive were highest, and FCR were lowest. Meanwhile, from d 28 to 42, there was no significant differencein the growth performance between POL-0.4 and POL-0.2. These results indicate that a higher dosage of herbal medicine as a feed additive does not always have better effects, which is consistent with the reports of Zhu et al. (2004). Table 2 shows significant differences in BW between different groups at d 42. However, a closer look at the results reveals that the SE of the control group was greater than the other groups. This is due to the greater variance in the BW among individuals in the control group, whereas the herbal-treated groups showedsmaller BW variance among individuals. The greater variance of BW in the control group may be caused by the stress of repeated handling in the experiment, indicating a potential antistress effect of the herb P. oleracea extracts (Wang and Yang, 2010a), and this
observation will be the focus of future research. The current study revealed that different additive dosages of P. oleracea extracts in daily ration would bring different effects on cecal Lactobacillus and E. coli (Table 3). On d 28, E. coli number of POL-0.2 and POL-0.4 was significantly lower than that of CON,whereas Bifidobacterium and Lactobacillus were higher than in CON. The results showed that using P. oleracea in broilers could achieve beneficial effects of intestinal microbiota, which is in agreement with the opinions of other researchers. Wang et al. (1999) and Ke et al. (2003) reported that P. oleracea extract additives in daily ration could promote the increase of the broiler intestinal Lactobacillus and Bifidobacterium and restrain
the growth of E. coli and Salmonella. Zhang and Bao (2006) reported that oligosaccharide in P. oleracea had functions of promoting the growth of Bifidobacterium in the intestine, improving the intestinal flora structure and inhibiting the formation of harmful metabolic byproducts.
In this experiment, P. oleracea extracts on intestinal microecology reduced the population of E.
coli and increased the populations of Lactobacillus and Bifidobacterium, and also improve growth performance of birds. However, the values of microorganism population were small at the time of the experiment, which is consistent with the change of pH of ileum and cecum contents. These results indicated that there may be other mechanisms for P. oleracea extracts in improving growth. Nevertheless, the mechanism of P. oleracea improving the intestinal flora structure remains unclear; it has been suggested that P. oleracea could be an alternative to the use of antibiotics as growth promoters in poultry production. The results of growth performance and microbial populations have shown that with increased dosages of P. oleracea extracts, more is not always better. Adding 0.2% P. oleracea extracts to broiler feeds improved BWG and decreased FCR. The extracts could also increase the populations of the beneficial bacteria Lactobacillus
and Bifidobacterium in the cecum and resulted in a major reduction in E. coli. The growth-promoting effect of P. oleracea extracts is related to its effect of improving the intestinal microecology. However, there may be some other mechanisms of which we are not aware such as an anti-stress effect, which remain to be confirmed by further study.
ACKNOWLEDGMENTS
This study was financially supported by the Ministry of Science and Technology of China (No.
2011BAD34B02).
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